HomeMy WebLinkAboutENGINEERING LETTER - 17-00745 - 621 Eaglewood Dr - Solar PanelTo: Blue Raven Solar
1220 S. 630 E Ste. 430
American Fork, UT 84003
Subject: Certification Letter
Johnson Residence
621 Eaglewood Drive
Rexburg, ID. 83440
To Whom It May Concern,
The spacing of the solar standoffs should be kept at 48" o.c. with a staggered pattern to ensure proper distribution of loads.
November 27, 2017
A jobsite observation of the condition of the existing framing system was performed by an audit team from Blue Raven
Solar. All attached structural calculations are based on these observations and the design criteria listed below.
On the above referenced project, the roof structural framing has been reviewed for additional loading due to the
installation of the solar PV addition to the roof. The structural review, including the plans and calculations only apply to the
section of the roof that is directly supporting the solar PV system and its supporting elements. The observed roof framing is
described as follows.
The roof structure of (MP1) consists of composition shingle on roof plywood that is supported by pre‐manufactured trusses
that are spaced at @ 24"o.c.. The top chords, sloped at 27 degrees, are 2x4 sections, the bottom chords are 2x4 sections
and the web members are 2x4 sections. The truss members are connected by steel gusset plates. The max unsupported
projected horizontal top chord span is approximately 6'‐0''.
The roof structure of (MP2&3) consists of composition shingle on roof plywood that is supported by pre‐manufactured
trusses that are spaced at @ 24"o.c.. The top chords, sloped at 27 degrees, are 2x4 sections, the bottom chords are 2x4
sections and the web members are 2x4 sections. The truss members are connected by steel gusset plates. The max
unsupported projected horizontal top chord span is approximately 6'‐3''.
The existing roof framing system of (MP1) is judged to be adequate to withstand the loading imposed by the installation of
the solar panels. No reinforcement is necessary. Where required for standoff attcahments, install a vertical2x4 block
between adjecent trusses. Attach block to trusses per detail.
The existing roof framing system of (MP2&3) is judged to be adequate to withstand the loading imposed by the installation
of the solar panels. No reinforcement is necessary.
Johnson Residence, Rexburg, ID 1
Design Criteria:
● Applicable Codes = 2009 IBC/IRC, ASCE 7‐05
● Roof Dead Load = 7 psf (MP1) ‐‐ 7 psf (MP2&3)
● Roof Live Load = 20 psf
● Wind Speed = 90 mph, Exposure C
●
Sincerely,
Paul Zacher, P.E.
Project Engineer
Ground Snow Load = 50 psf ‐ Roof Snow Load = 35 psf
Please contact me with any further questions or concerns regarding this project.
Johnson Residence, Rexburg, ID 2
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FOETAT
S OHADI
DESNECIL
EXP. 08/31/2018
Gravity Loading
50 psf
(ASCE7 - Eq 7-1)
1 (ASCE7 - Table 7-2)
1 (ASCE7 - Table 7-3)
1
35.0 psf
(ASCE7 - Eq 7-2)
1
35.0 psf
3.0 psf
4.00 ft
2.67 ft
10.68 sft
32 lb
4.00
2.00
0.73
0.00 (Ceiling Not Vaulted)
0.27
7.0 psf
7.9 psf
4.00
2.00
0.73
0.00 (Ceiling Not Vaulted)
0.27
7.0 psf
7.86
PV Dead Load = 3 psf (Per Blue Raven Solar)
DL Adjusted to 27 Degree Slope
Point Loads of Standoffs
DL Adjusted to 27 Degree Slope
Miscellaneous
Vaulted Ceiling
Roof Live Load = 20 psf
Roof Plywood
Roof Dead Load (MP1)
Composition Shingle
Note: Roof live load is removed in area's covered by PV array.
Roof Snow Load Calculations
pg = Ground Snow Load =
Ce = Exposure Factor =
pf = 0.7 Ce Ct I pg
Ct = Thermal Factor =
I = Importance Factor =
Cs = Slope Factor =
Standoff Tributary Area =
ps = Cspf
ps = Sloped Roof Snow Load =
pf = Flat Roof Snow Load =
PV System Weight
Weight of PV System (Per Blue Raven Solar)
X Standoff Spacing =
Y Standoff Spacing =
Note: PV standoffs are staggered to ensure proper distribution of loading
Roof Plywood
Vaulted Ceiling
2x4 Top Chords @ 24"o.c.
2x4 Top Chords @ 24"o.c.
Miscellaneous
Total Roof DL (MP2&3)
Total Roof DL (MP1)
Roof Dead Load (MP2&3)
Composition Shingle
Johnson Residence, Rexburg, ID 3
Wind Calculations
90 mph
C
Gable/Hip
27 degrees
20 ft
17.4 ft
(Eq_6-15)
0.9 (Table 6-3)
1 (Fig. 6-4)
0.85 (Table 6-4)
90 mph
1 (Table 6-1)
qh = 15.86
Zone 1 Zone 2 Zone 3 Positive
GCp = -0.85 -1.45 -2.30 0.40 (Fig. 6-11)
Uplift Pressure = -13.47 psf -22.95 psf -36.42 psf 10.0 psf (Minimum)
X Standoff Spacing = 4.00 4.00 2.67
Y Standoff Spacing = 2.67 2.67 2.67
Tributary Area = 10.68 10.68 7.12
Footing Uplift = -144 lb -245 lb -259 lb
-259 lb
400 lb
Therefore, OK
Fastener =1 - 5/16" dia Lag
Number of Fasteners = 1
Embedment Depth = 2.25
Pullout Capacity Per Inch = 250 lb
Fastener Capacity = 563 lb
w/ F.S. of 1.5 = 376 lb
Therefore, OK
Input Variables
Wind Speed
Effective Wind Area
Design Wind Pressure Calculations
Roof Shape
Standoff Uplift Calculations
Roof Slope
376 lb capacity > 259 lb demand
Maximum Design Uplift =
Standoff Uplift Capacity =
400 lb capacity > 259 lb demand
Fastener Capacity Check
Standoff Uplift Check
Kz (Exposure Coefficient) =
Kzt (topographic factor) =
Kd (Wind Directionality Factor) =
V (Design Wind Speed) =
Importance Factor =
qh = 0.00256 * Kz * Kzt * Kd * V^2 * I
Wind Pressure P = qh*G*Cn
Exposure Category
Per ASCE 7-05 Components and Cladding
Mean Roof Height
Johnson Residence, Rexburg, ID 4
Framing Check
(MP1)PASS
Dead Load 7.9 psf
PV Load 3.0 psf
Snow Load 35.0 psf
Governing Load Combo = DL + SL
Total Load 45.9 psf
Fb (psi) = f'b x Cd x Cf x Cr (NDS Table 4.3.1)
900 x 1.15 x 1.5 x 1.15
Allowed Bending Stress = 1785.3 psi
(wL^2) / 8
= 412.707 ft#
= 4952.48 in#
Actual Bending Stress = (Maximum Moment) / S
= 1617.2 psi
L/180 (E = 1600000 psi Per NDS)
= 0.4 in
Deflection Criteria Based on =
(w*L^4) / (185*E*I)
=
= L/554 > L/180 Therefore OK
Allowed Deflection (Live Load) =L/240
0.3 in
(w*L^4) / (185*E*I)
L/728 > L/240 Therefore OK
Member Area = Fv (psi) = 180 psi (NDS Table 4A)
Allowed Shear = Fv * A = Max Shear (V) = w * L / 2 = 275 lb
Check Bending Stress
Continuous Span
0.130 in
0.099 in
Member Properties
Member Size
2x4
S (in^3)
3.06 DF#2
Member Spacing
@ 24"o.c.
Maximum Moment =
Check Deflection
I (in^4)
5.36
Lumber Sp/Gr
Actual Deflection (Live Load) =
Allowed Deflection (Total Load) =
Actual Deflection (Total Load) =
Allowed > Actual -- 90.6% Stressed -- Therefore, OK
945 lb
Allowed > Actual -- 29.2% Stressed -- Therefore, OK
(True Dimensions)
5.3 in^2
Check Shear
w = 92 plf
2x4 Top Chords @ 24"o.c.
Member Span = 6' - 0"
Johnson Residence, Rexburg, ID 5
Framing Check
(MP2&3)PASS
Dead Load 7.9 psf
PV Load 3.0 psf
Snow Load 35.0 psf
Governing Load Combo = DL + SL
Total Load 45.9 psf
Fb (psi) = f'b x Cd x Cf x Cr (NDS Table 4.3.1)
900 x 1.15 x 1.5 x 1.15
Allowed Bending Stress = 1785.3 psi
(wL^2) / 8
= 447.815 ft#
= 5373.78 in#
Actual Bending Stress = (Maximum Moment) / S
= 1754.8 psi
L/180 (E = 1600000 psi Per NDS)
= 0.416 in
Deflection Criteria Based on =
(5*w*L^4) / (384*E*I)
=
= L/204 > L/180 Therefore OK
Allowed Deflection (Live Load) =L/240
0.312 in
(5*w*L^4) / (384*E*I)
L/267 > L/240 Therefore OK
Member Area = Fv (psi) = 180 psi (NDS Table 4A)
Allowed Shear = Fv * A = Max Shear (V) = w * L / 2 = 287 lb
Simple Span
0.281 in
0.368 in
945 lb
Allowed > Actual -- 30.4% Stressed -- Therefore, OK
Check Bending Stress
Maximum Moment =
Allowed > Actual - 98.3% Stressed -- Therefore, OK
Check Deflection
Allowed Deflection (Total Load) =
Actual Deflection (Total Load) =
Actual Deflection (Live Load) =
(True Dimensions)
w = 92 plf
2x4 Top Chords @ 24"o.c.
Member Span = 6' - 3"
Member Properties
Member Size S (in^3) I (in^4) Lumber Sp/Gr Member Spacing
2x4 3.06 5.36 DF#2 @ 24"o.c.
Check Shear
5.3 in^2
Johnson Residence, Rexburg, ID 6
Lateral Check
Level Area Weight (psf) Weight (lb)
Roof 3000 sf 7.9 psf 23569 lb
Ceiling 3000 sf 6.0 psf 18000 lb
7/8" Stucco 100 ft 11.0 psf 4400 lb (8'-0" Wall Height)
Int. Walls 100 ft 6.4 psf 2560 lb
48529 lb
3.0 psf
348 sf
1044 lb
4853 lb
1044 lb
2.2%
4853 lb > 1044 lb, Therefore OK
Per 2009 IBC Chapter 34
Existing Weight of Effected Building
Existing Weight of Effected Building
Proposed Weight of PV System
Weight of PV System (Per Blue Raven Solar)
Approx. Area of Proposed PV System
Approximate Total Weight of PV System
10% Comparison
10% of Existing Building Weight (Allowed)
Approximate Weight of PV System (Actual)
Percent Increase
Johnson Residence, Rexburg, ID 7